It has been well established that interactions between cells and the extracellular matrix (ECM) play very important roles in cell proliferation, differentiation and multiple stages of tumor development. Fibronectin (FN) is a major structural and functional component of the ECM. Recent studies have shown that alterations in FN matrix composition can have dramatic effects on cell behaviors. Two mutant FNs which will be focused on in this proposal have been mutated at two sites in the cell binding domain, the RGD cell binding site (FN(RGD-)) and the nearby synergy site (FN(syn-)). These two mutant FNs form fibrillar matrices in the presence of native FN. However, inclusion along with native FN of either mutant FN can dramatically perturb adhesion, spreading and migration of cells on these matrices and causes defects in amphibian development. In this proposal, a series of in vitro assembled chimeric matrices composed of different ratios of mutant versus native FN will be developed. The alterations of cell behaviors including spreading and migration will be analyzed with cells plated on those matrices. The signaling pathways involved in those processes will be characterized. This study may provide insights into a novel mechanism for regulating cell functions and tumor invasion by sequestration or exposure of FN cell binding sites by ECM reorganization.